The project seeks to develop efficient means to rapidly assay different portions of a receptor sequence as candidates for interacting with intracellular proteins. This is accomplished by making a large number of short peptides with sequences corresponding to different portions of the receptor. Further, once a particular peptide has been characterized by biological assays as being a good ligand, we synthesize the sequence with stable isotope labeled amino acids to enable us to determine the bound form of these ligands with their binding proteins in solution using NMR spectroscopy. Mass spectrometry is a method of choice to unambiguously confirm the identity of some of the peptides in question, due to either complex solution equilibria or contaminants not separable by HPLC.